lib/krb5/kuserok.c

   1 /*
   2  * Copyright (c) 1997 - 2005 Kungliga Tekniska Högskolan
   3  * (Royal Institute of Technology, Stockholm, Sweden).
   4  * All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  *
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  *
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  *
  17  * 3. Neither the name of the Institute nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  */
  33
  34 #include "krb5_locl.h"
  35 #include <dirent.h>
  36
  37 /* see if principal is mentioned in the filename access file, return
  38    TRUE (in result) if so, FALSE otherwise */
  39
  40 static krb5_error_code
  41 check_one_file(krb5_context context,
  42                const char *filename,
  43                struct passwd *pwd,
  44                krb5_principal principal,
  45                krb5_boolean *result)
  46 {
  47     FILE *f;
  48     char buf[BUFSIZ];
  49     krb5_error_code ret;
  50     struct stat st;
  51
  52     *result = FALSE;
  53
  54     f = fopen (filename, "r");
  55     if (f == NULL)
  56         return errno;
  57     rk_cloexec_file(f);
  58
  59     /* check type and mode of file */
  60     if (fstat(fileno(f), &st) != 0) {
  61         fclose (f);
  62         return errno;
  63     }
  64     if (S_ISDIR(st.st_mode)) {
  65         fclose (f);
  66         return EISDIR;
  67     }
  68     if (st.st_uid != pwd->pw_uid && st.st_uid != 0) {
  69         fclose (f);
  70         return EACCES;
  71     }
  72     if ((st.st_mode & (S_IWGRP | S_IWOTH)) != 0) {
  73         fclose (f);
  74         return EACCES;
  75     }
  76
  77     while (fgets (buf, sizeof(buf), f) != NULL) {
  78         krb5_principal tmp;
  79         char *newline = buf + strcspn(buf, "\n");
  80
  81         if(*newline != '\n') {
  82             int c;
  83             c = fgetc(f);
  84             if(c != EOF) {
  85                 while(c != EOF && c != '\n')
  86                     c = fgetc(f);
  87                 /* line was too long, so ignore it */
  88                 continue;
  89             }
  90         }
  91         *newline = '\0';
  92         ret = krb5_parse_name (context, buf, &tmp);
  93         if (ret)
  94             continue;
  95         *result = krb5_principal_compare (context, principal, tmp);
  96         krb5_free_principal (context, tmp);
  97         if (*result) {
  98             fclose (f);
  99             return 0;
 100         }
 101     }
 102     fclose (f);
 103     return 0;
 104 }
 105
 106 static krb5_error_code
 107 check_directory(krb5_context context,
 108                 const char *dirname,
 109                 struct passwd *pwd,
 110                 krb5_principal principal,
 111                 krb5_boolean *result)
 112 {
 113     DIR *d;
 114     struct dirent *dent;
 115     char filename[MAXPATHLEN];
 116     krb5_error_code ret = 0;
 117     struct stat st;
 118
 119     *result = FALSE;
 120
 121     if(lstat(dirname, &st) < 0)
 122         return errno;
 123
 124     if (!S_ISDIR(st.st_mode))
 125         return ENOTDIR;
 126
 127     if (st.st_uid != pwd->pw_uid && st.st_uid != 0)
 128         return EACCES;
 129     if ((st.st_mode & (S_IWGRP | S_IWOTH)) != 0)
 130         return EACCES;
 131
 132     if((d = opendir(dirname)) == NULL)
 133         return errno;
 134
 135     {
 136         int fd;
 137         struct stat st2;
 138
 139         fd = dirfd(d);
 140         if(fstat(fd, &st2) < 0) {
 141             closedir(d);
 142             return errno;
 143         }
 144         if(st.st_dev != st2.st_dev || st.st_ino != st2.st_ino) {
 145             closedir(d);
 146             return EACCES;
 147         }
 148     }
 149
 150     while((dent = readdir(d)) != NULL) {
 151         if(strcmp(dent->d_name, ".") == 0 ||
 152            strcmp(dent->d_name, "..") == 0 ||
 153            dent->d_name[0] == '#' ||                      /* emacs autosave */
 154            dent->d_name[strlen(dent->d_name) - 1] == '~') /* emacs backup */
 155             continue;
 156         snprintf(filename, sizeof(filename), "%s/%s", dirname, dent->d_name);
 157         ret = check_one_file(context, filename, pwd, principal, result);
 158         if(ret == 0 && *result == TRUE)
 159             break;
 160         ret = 0; /* don't propagate errors upstream */
 161     }
 162     closedir(d);
 163     return ret;
 164 }
 165
 166 static krb5_boolean
 167 match_local_principals(krb5_context context,
 168                        krb5_principal principal,
 169                        const char *luser)
 170 {
 171     krb5_error_code ret;
 172     krb5_realm *realms, *r;
 173     krb5_boolean result = FALSE;
 174
 175     /* multi-component principals can never match */
 176     if(krb5_principal_get_comp_string(context, principal, 1) != NULL)
 177         return FALSE;
 178
 179     ret = krb5_get_default_realms (context, &realms);
 180     if (ret)
 181         return FALSE;
 182
 183     for (r = realms; *r != NULL; ++r) {
 184         if(strcmp(krb5_principal_get_realm(context, principal),
 185                   *r) != 0)
 186             continue;
 187         if(strcmp(krb5_principal_get_comp_string(context, principal, 0),
 188                   luser) == 0) {
 189             result = TRUE;
 190             break;
 191         }
 192     }
 193     krb5_free_host_realm (context, realms);
 194     return result;
 195 }
 196
 197 /**
 198  * This function takes the name of a local user and checks if
 199  * principal is allowed to log in as that user.
 200  *
 201  * The user may have a ~/.k5login file listing principals that are
 202  * allowed to login as that user. If that file does not exist, all
 203  * principals with a first component identical to the username, and a
 204  * realm considered local, are allowed access.
 205  *
 206  * The .k5login file must contain one principal per line, be owned by
 207  * user and not be writable by group or other (but must be readable by
 208  * anyone).
 209  *
 210  * Note that if the file exists, no implicit access rights are given
 211  * to user@@LOCALREALM.
 212  *
 213  * Optionally, a set of files may be put in ~/.k5login.d (a
 214  * directory), in which case they will all be checked in the same
 215  * manner as .k5login.  The files may be called anything, but files
 216  * starting with a hash (#) , or ending with a tilde (~) are
 217  * ignored. Subdirectories are not traversed. Note that this directory
 218  * may not be checked by other Kerberos implementations.
 219  *
 220  * @param context Kerberos 5 context.
 221  * @param principal principal to check if allowed to login
 222  * @param luser local user id
 223  *
 224  * @return returns TRUE if access should be granted, FALSE otherwise.
 225  *
 226  * @ingroup krb5_support
 227  */
 228
 229 krb5_boolean KRB5_LIB_FUNCTION
 230 krb5_kuserok (krb5_context context,
 231               krb5_principal principal,
 232               const char *luser)
 233 {
 234     char *buf;
 235     size_t buflen;
 236     struct passwd *pwd;
 237     krb5_error_code ret;
 238     krb5_boolean result = FALSE;
 239
 240     krb5_boolean found_file = FALSE;
 241
 242 #ifdef POSIX_GETPWNAM_R
 243     char pwbuf[2048];
 244     struct passwd pw;
 245
 246     if(getpwnam_r(luser, &pw, pwbuf, sizeof(pwbuf), &pwd) != 0)
 247         return FALSE;
 248 #else
 249     pwd = getpwnam (luser);
 250 #endif
 251     if (pwd == NULL)
 252         return FALSE;
 253
 254 #define KLOGIN "/.k5login"
 255     buflen = strlen(pwd->pw_dir) + sizeof(KLOGIN) + 2; /* 2 for .d */
 256     buf = malloc(buflen);
 257     if(buf == NULL)
 258         return FALSE;
 259     /* check user's ~/.k5login */
 260     strlcpy(buf, pwd->pw_dir, buflen);
 261     strlcat(buf, KLOGIN, buflen);
 262     ret = check_one_file(context, buf, pwd, principal, &result);
 263
 264     if(ret == 0 && result == TRUE) {
 265         free(buf);
 266         return TRUE;
 267     }
 268
 269     if(ret != ENOENT)
 270         found_file = TRUE;
 271
 272     strlcat(buf, ".d", buflen);
 273     ret = check_directory(context, buf, pwd, principal, &result);
 274     free(buf);
 275     if(ret == 0 && result == TRUE)
 276         return TRUE;
 277
 278     if(ret != ENOENT && ret != ENOTDIR)
 279         found_file = TRUE;
 280
 281     /* finally if no files exist, allow all principals matching
 282        <localuser>@<LOCALREALM> */
 283     if(found_file == FALSE)
 284         return match_local_principals(context, principal, luser);
 285
 286     return FALSE;
 287 }